Opioid addiction from the chronic use of prescription analgesics and illicit agents represents a major unmet public health crisis. Current pharmacotherapies for opioid dependence, such as opioid maintenance therapy (e.g., methadone and buprenorphine), reduce the need for illicit substances and alleviate opioid withdrawal, but possess a similar side effect profile as other opioids and can also trigger severe opioid withdrawal responses. Consequently, a strong need remains for the development of new treatment strategies that would relieve patients of opioid dependence without transferring this dependency to another drug. D9-tetrahydrocannabinol (THC), the primary psychoactive constituent in Cannabis sativa, has long been known to reduce naloxone- precipitated withdrawal symptoms in opioid-dependent animals. However, THC and other CB1 receptor agonists display several cannabimimetic side effects, including marijuana-like subjective activity, that limit their general therapeutic potential. Alternatively, increasing brain levels of the endogenous cannabinoids anandamide and 2-arachidonylglycerol (2-AG) though the blockade of their respective catabolic enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) represents a promising therapeutic approach that lacks many of the undesirable side effects of direct-acting CB1 receptor agonists. We have recently developed JZL184, the first highly potent, selective, and orally active MAGL inhibitor. This compound causes significant elevations in brain 2-AG levels and robustly reduces the magnitude of naloxone-precipitated somatic withdrawal responses in morphine-dependent mice, but elicits far fewer cannabimimetic effects compared with THC. While FAAH inhibitors produce significant effects in preclinical models of pain and anxiety, our preliminary data show that these compounds lack efficacy in reducing opioid withdrawal effects. Thus, the overall objective of this proposal is to test whether optimized MAGL inhibitors will reduce the constellation of withdrawal symptoms in opioid-dependent mice and rhesus monkeys undergoing abstinence. In the proposed experiments, we will characterize the metabolism, pharmacokinetics, target selectivity, safety profile, and effectiveness of JZL184 and structurally related analogues in ameliorating withdrawal symptoms in established rodent and nonhuman primate models of opioid dependence. The following three major hypotheses will be tested: 1) MAGL inhibitors will reduce somatic and affective withdrawal signs in opioid- dependent rodents; 2) MAGL inhibitors will reduce opioid withdrawal symptoms and withdrawal-related increases in heroin self-administration in opioid-dependent rhesus monkeys; and 3) inhibition of MAGL will produce minimal side effects compared to direct opioid and cannabinoid receptor agonists. The ultimate goal of this application is to identify a potent, selective, orally active, safe, and efficacious MAGL inhibitor that prevents opioid withdrawal in mouse and monkey preclinical models and is ready for IND-enabling toxicology en route to clinical development as a novel therapeutic for treating opioid abuse.